Grinding machine



Oct. 9, 1945. F. c. JEARUM 2,385,687 I GRINDING MACHINE Filed May 25.1945 ISSheets-Shet 1 In v 611/602 F C. Jearzom /Mum Oct. 9, 1945. F. c.JEARUM GRINDING MACHINE Filed May 25, 1943 3 Sheets-Sheet 3 PatentedOct. 9, 1945 UNITED GRINDING MACHINE Frederick Charles J earum, Sutton,England Application May 25, 1943, Serial No. 488,452 In Great BritainJune 12, 1942 12 Claims.

This invention relates to the grinding, lapping, cutting or polishingupon a skaif or rotary disc (hereinafter referred to as cutting) ofdiamonds or of other stones, compositions or hard tool metals(hereinafter referred to as stones) to generate forms requiring thecontinuous or step rotation about the axis of the stone such as forexample conical forms with or without radiussed points or (to generate)domed or convex forms or (to produce) pyramidal or domed faceted forms;these terms including not only complete forms but frustums and alsoforms having a facet or facets which if appropriately repeated wouldproduce a pyramid or pyramidal frustum. The invention is applicable tothe production of stone forms for industrial tool making or for thejewelry trade.

The object of the present invention is to provide a machine forautomatically or semi-automatically generating or cutting forms of thekind indicated, which is adapted for repetition work or mass productionof a selected form of stone or certain selected forms with a very highdegree of accuracy.

The invention consists in a machine for cutting stones to generate formsof the kind indicated comprising means adapted to rotate a stone orenable it to be rotated from one cutting contact position to anotherabout its axis and means adapted to enable the said stone axis to berevolved about an axis intersecting the stone axis in the plane of theskaif employed for cutting and in such a manner as to generate a conicalfigure which is tangent to a line normal to the skaif. This axis aboutwhich the stone axis may be revolved may be conveniently referred tohereinafter as the"tangent axis.

The angular position of the tangent axis may be expressed with respectto the normal to the skaif plane as rte-i) where y is the apex orincluded angle of the form to be generated about the stone axis.

Locking or index setting means may be provided with respect to therotation about the stone or tangent axis so that continuous or stepwiserotation may be effected about the stone axis, or'so that the stone axismay be continuously revolved about the tangent axis or maintainedstationary. Also means may be provided, in a machinadapted to revolveboth axes about an axis normal to the skaif for automatically cuttingdiamonds, for locking the mounting so that said axes do not revolveabout the normal axis when suchmachine is used for stones other thandiamonds.

The structure of a diamond is such that it is capable ofbeing out onlywhen the abrasive particles pass in a certain directional sense relativeto the grain or crystalline structure of the diamond known as thecutting or polishing grain. The usual practice in the trade has been todetermine the correct cutting grain or direction by the observation andskill of the operative. It is however known or it has been proposed toprovide a machine adapted automatically to find the cutting grain of thediamond by employing a rotary skaif or cutting disc, the axis of whichis revolved in a planetary or orbital path such that the cutting grainof the diamond operated upon is automatically found at least twice ineach revolution of the skaif about the planetary axis. It will beappreciated, therefore, that when the invention is applied to'a machinefor cutting diamonds solely or in addition to other stones it must beused in conjunction with means for automatically finding the cuttinggrain of the diamond. To this end a skaif having a planetary or orbitalpath such as indicated above may be employed, although it is preferredaccording to a further feature of the invention to provide a novelselfcontained grain-finding means by revolving the stoneand tangent axesreferred to above about an axis normal to the skaif and preferablyintersecting the said axes in the plane of the skaif or cutting disc.

The accompanying drawings illustrate three examples of the inventionshowing the head of a machine for generating conical points of differentangles or other forms based on such angles. The means for supporting thehead over a skaif are not illustrated as such form no part of theinvention and any appropriate arbor means of known character may beemployed.

In the accompanying drawings:

Figure 1 is a sectional elevation of a machine head according to theinvention for generating conical points or like forms where the apex orincluded angle is 50.

Figures 2 and 3 are similar sectional elevations of heads for generatingconical points and like forms where the apex or included angle isrespectively 55 and Figures 2 and 3 also illustrate certainmodifications of the manner in which the invention may be carried intoeffect.

Figures 1, 2 and 3 illustrate examples of selfcontained means forrevolving the stone and tangent axes about an axis normal to the skaifIn carrying the invention into effect'according to one mode as describedwith reference to Figure 1 for generating any of the forms above menwithits axis A normal to the horizontal skaif 2.

The shaft 3 may be supported on a thrust bearing indicated by thegeneral reference 4 comprising a thrust collar 4a resiliently supportedon a plurality of equally spaced spring-pressed plung-- v ers 4b. Theshaft is screw-threaded at its upper end to receive a nut member 40which bears upon the thrust collar 4a and is provided with a'lock nut4d. A chain wheel 5 (or other gear) is provided on the end of the shaftand a chain 5a is adapted to cause its rotation at a suitable speed,power being supplied from any suitable source (not shown). At the lowerend of the shaft an angle plate 6 is mounted so that it may be rotatedwith the shaft 3. The angle plate comprises a part at right-angles tothe axis of the shaft and a part Be at an angle thereto (in the instanceunder consideration) of 147 so that it lies bevel gear 8, having teeth(in this case), is

rotatably mounted and driven by a chain wheel 8a (or other gear) so thatrotation may be communicated by the bevel gear 8 for revolving the stoneaxis C in a' path which generates a conical surface of revolution (towhich the vertical axis A is tangent) about the-tangent axis B.

In the angled portion 6a of the plate 6 in a suitable bearin bushing asleeve 9 carrying at the underside of the plate a bevel gear I 0 having40 teeth is rotatably mounted. Fixed upon the sleeve 9 at the upper sideof the angled plate 611 is a. (id-toothed bevel gear H which meshes withthe bevel gear I. 7 I2 is rotatably mounted having fixed at its upperend a -toothed bevel gear [3 meshing with the gear 8. At its lower. endthe spindle 12 carries a dop carrier or; head 12a having an angularlydisposed face or bed I21) for receiving the bushing or body of thestone-holder or dop 14. Any suitable means may; be provided for securingthe dop upon its bed. This bed is located at an angle to accord with theangleat which the stone axis is located. In this instance it will beappreciated that the angle included between the stone axis and the planeof the skaif will be 25, that is to say half that of the included angleof the conical or other forms to be generated. g

The axis of the spindle |2,.(w hich is the tangent axis B previouslymentioned) is located so that it intersects the stone axis 0 in theplane of the skaif 2 and also intersects the vertical axis A at the samepoint.

.The angle a: included between the tangent axis Within the sleeve 9, aspindle B and the vertical axis A and the angle between the axis B andthe stone axis C is 32 30, the angle included between the stone axis andthe vertical axis being twice this amount, which leaves the angle of 25above mentioned as .the included angle between the stone angle and theplane of the skaif, that is to say, half the included angle y of thestone form to be generated, which in this case is 50.

It "will be appreciated that to find the angle a: for any form having anincluded angle y the formula tioned of which the included angle is 50the end I l of an arbor mounted over a horizontal skaif 2 has a mainshaft 3 mounted in suitable bearings may be employed, the angle beingthe angle the stone axis C makes with the plane of the skaif 2.

The tool-holder or dop l4 may be of any known kind and has a spindle Mafor enabling the stone l5 to be rotated about its axis 0' and also meansoperated by a milled knob Mb for affording the stone' an axialdisplacement for feed, retraction, setting or like purposes. Upon therotatable spindle Ma a 36-toothed bevel gear I6 is fixed in mesh withthe bevel I0 on the sleeve 9. Means for locking the gear I 6 againstrotation is provided, which may consist of a pin 18a adapted to beinserted in any selected bore of a series I6b with which the gear I6 isprovided and engaged in a recess on the block or head l2a. The series ofbores [6b may be arranged according to a dividing index for setting thestone stepwise for cutting predetermined facets.

The plate 6 may be provided with set screws l1, l8 for respectivelylocking in any of the teeth of the ears 'l and 8. The lock upon the gearI may be used as a supplementary lock or as an alternative, lock to thepin device Ilia and may be used for facet cutting while the look uponthe gear 8 serves to anchor the spindle l2 and prevent rotation of thestone axis C about the tangent axis B when grinding facets.

Similar means 50 may be provided for locking the chain wheel 5 whenrevolution of the head l2d about the vertical axis is not required, asfor example when grinding stones (other than diamonds) which have 'noparticular cutting grain. e I I In association with the locking meansfor preventing rotation of the stone about its axis C or its revolutionabout th tangent axis B or the revolution of the head lZa about thevertical axis A, a slip friction clutch or a disengageable clutch isemployed on each of the means for driving the chains of the wheels 5, Iand 8. p

From the above it will be appreciated that by driving the verticalspindle 3 the angle plate 6, 6a is caused to revolve about the verticalaxis A together with the tangent axis spindle l2 and tool-holder head120. so that the axis B of the spindle generates a coneof revolution theaxis of which coincides with the vertical axis. This movement inconjunction with the rotation of the skaif.2;ensures that the cuttinggrain of the stone is found twice in each revolution. If while this 1 istakingplace the gear bevel I on the vertical bevel gear It on the dop islocked a. 50 pyramidal facet'will be out upon the stone and a series ofpyramidal facets may be cut by turning spindle Ma and setting the stoneabout its axis through the appropriate angles by means of the pin I60,and the series of bores [6b, appropriate means being provided forpreventing the revolution of the axis C about the tangent axis whilecutting a facet or facets. For this purpose, if desired, a calibrateddividing head may be associated with the bores.

Assuming that it is desired to generate a radiussed point or dome shapeform, in addition to the rotation of the stone about its own axis C andthe revolution of the stone axis about the vertical axis A, a drive iscommunicated to the bevel gear 8 on the vertical spindle which drivesthe bevel gear IS on the tangent axis spindle it which causes the headIn in which the dop is mounted bodily to be revolved about the tangentaxis B so that the axis C of the stone generates a cone of revolution towhich a plane including the vertical axis A is tangent. The radiussedpoint or dome will be tangential to planes having an included angle of50 and the diameter of the point or dome will depend upon the distancethe apex of the cone of the stone is set backfrom the point ofintersection of its axis with the tangent axis B, the setting backoperation being accomplished by adjusting the axial feed means of thedop as by manipulating the knob [41). The revolution of the stone axis Cabout the tangent axis B will progressively raise the stone axis fromthe position seen in the drawings to the Vertical and as the revolutioncontinues the stone axis will be progressively lower again. This motionin conjunction with the rotation of the stone on its own axis C willcause a true spherical point or dome to be generated by the cuttingaction of the skaif.

In carrying the invention into effect according to a modification, asexemplified in Figure 2 for generating forms having a 55 included angle,the vertical spindle 3 (the lower part only of which is illustrated)carrying an angled plate 6, 5a similar to that already described but setat an angle corresponding with the angle required for the tangent axis B(according to the basic. included angle of the form to be out) hasmounted upon it a bevel gear 8 (of 83 teeth) which may be chain orotherwise driven, while the tangent axis spindle l2 carrying thetool-holding head l2a has a bevel gear l3 (with 28 teeth) fixed upon itfor revolving the head and stone axis C so that the latter generates theconical surface which is tangent to the vertical axis A of the shaft.Locking means may be provided for preventing rotation about the tangentaxis similar to the locking means provided for the gear 8 as describedin reference to Figure 1 and as shown in Figure 3.

Between the angled plate and the head I20. a 38- toothed bevel gear [0carried on the sleeve 9 meshes with a 35-toothed bevel gear I6 on thedop spindle. In this modification, instead of driving the dop spindlefrom a gear (such as I, Figure 1) on the main vertical spindle a driveis communicated through a pinion I l a on the sleeve. The pinion Ila has25 teeth and meshes with a 28-toothed spur wheel l9 having a stub shaftmounted in the plate portion 6a. This gear is provided with a couplingor means adapted to receive an independent flexible or cable drive l9areceiving power from any suitable source. For the purpose of locking thedop spindle in any position afiorded by 'the teeth of the 28-toothedspur gear l9 for facet cutting, a spring-pressed or screw-threadedplunger 20 is suitably mounted upon the angled plate so that the nose ofthe plunger may engage between any selected pair of teeth on' the spurgear. The axis B is disposed so that the angle included between it andthe vertical axis A is 3115 while the angle included between the dopaxis 0 and the plane of the skaif 2 is 2730 for forming a cone orpyramid of an included angle of 55.

In carrying the invention into efiect (see Figure 3) for generatingforms having a greater included angle such as, say, that of for example,the vertical spindle 3 carries, rotatably mounted upon it, a chain orotherwise driven bevel gear 8 having 25 teeth. A locking pin l8 forengaging the teeth of the bevel gear may be provided on the angled plateadjacent the vertical spindle. A bevel gear l3 of 22 teeth is mounted onthe upper end of the head or tangent axis spindle l2 and is in mesh withthe bevel gear 8. The dop spindle carries a IS-toothed bevel gear I6meshing with a bevel gear I0 having the same number of teeth carried bythe sleeve 9. Between the gear l3 and the angled plate, a spur gear H ahaving 19 teeth is provided and meshes with a spur gear 19 of 20 teethrotatable in a bushing in the angled plate, which also carries a lockingpin or plunger 20 for engaging the spur teeth as described in thepreceding modification. The spur gear I!) has a coupling for a flexibleor cable drive l9a.

In the form of the invention shown in Figure 3 means may be provided (asin the cases described in reference to Figures 1 and 2) for looking thevertical shaft 3 to a fixture or otherwise preventing rotation of thehead l2a about the vertical axis A.

It will be appreciated that in each of the forms of the inventiondescribed, the means for imparting the various operational movementsconcerned in generating the several forms is designed for shapes of thepredetermined included angle specified, and that for shapes having otherincluded angles the operating means are appropriately designed orredesigned to dispose the dop or stone axis C and the head spindle ortangent axis B at the appropriate angles, and to provide gears havingthe appropriate number of teeth for effecting the required relativerotations.

It will also be appreciated that although certain forms or means havebeen described specifically in reference to a particular figure of thedrawings such may, circumstances permitting, be equally adopted inconnection with a form or modification described in another figure ofthe drawings.

Instead of revolving the angled plate around the axis of the verticalshaft a similar effect may be obtained when the angled plate ismaintained stationary, by employing in place of the skaif revolvingabout a fixed axis, a cutting disc or skaif mounted upon a crank orcrank disc, giving the skaif axis a planetary motion around the axis ofthe crank or crank disc as well as a rotation about its own axis.

In Figure 4 a planetary skaif arrangement is illustrated. The skaif 2 isrotatably mounted upon a crank pin (having an axis D) of the crank 22.The crankshaft 23 is mounted in a footstep bearing 24 carried by asuitable base 25 which may be in one with the base on which the arbor lis mounted. The crank 22 carries a large pulley 26 mounted coaxially ofthe axis E of the crankshaft 23, the pulley being driven by a belt 26afrom any suitable power source. The pulley 26 has suspended from itsunderside an electric motor 21 the shaft of which carries a pulley 28driving through the belt 28a, a pulley formation 29 on the crank pinmounting. The footstep bearing 24 carries externally an insulationannulus 30 having distributing rings 3|, 32 coupled by supply lines 33to a suitable source of E. M. F. A bracket on the motor 21 carriesbrushes 34, 35 which collect from the rings 3! and 32 respectively.According to this arrangement the skaif and skaif axis D are revolvedplanetwise by the pulley drive 25, 26a about the crank axis E, whilesimultaneously the skaif is rotated about its own axis D by the motor 21through the pulley 28, 29. A fragment of the dop I4 and the stone I5 areshown in cutting contact with the skaif.

It will be appreciated that when stones other than diamonds are to becut it is unnecessary to turn the stone or provide a relative motionbetween the skaif and the stone such that the cutting grains of theskaif pass in a diversity of directions with respect thereto in order tosecure a cutting action and consequently in such cases it is unnecessaryto provide any means such as had been described for automaticallyfinding the cutting grain. In cutting stones other than diamonds thearrangements described in reference to Figures 1, 2 and 3 may beemployed whilst maintaining the axes B and C stationary with respect toa vertical axis such as A and without employing a skaif planetaryarrangement such as shown in Figure 4:. It will however be understoodthat by providing for revolution about the axis A or providing theplanetary arrangement shown in Figure 4 a machine may be adapted foruniversal purposes, that is to say for grinding diamonds in addition toany otherstones.

I claim:

l. A machine for cutting stones to generate forms of the kind indicatedcomprising a skaif, means for rotating the skaif, means for continuouslyrotating a stone about its axis and means for continuously revolvingsaid stone axis about a tangent axis intersecting the stone axis in theplane of the skaif in such a manner that the stone axis moves through apath describing a, conical figure which is tangent to a line normal tothe surface of the skaif.

2. A machine as claimed in claim 1 wherein a driving gear is mountedwith its axis normal to the surface of the skaif and is meshed with agear coaxial with the tangent axis for revolving the stone axis aboutthe tangent axis.

3. A machine as claimed in claim 1 wherein means are provided forrevolving the stone and tangent axes together about an axis normal tothe surface of the skaif and intersecting the said axes in the plane ofthe skaif for enabling the machine automatically to cut diamonds inaddition to other stones.

'4. LA machine as claimedv in claim 1 in combination with a skaifrotatable about its axis and having means for revolving the skaif axisabout a planetary axis as an alternative to revolving the stone andtangent axes together about the axis normal: to the surface of theskaif, for enabling the machine automatically to cut diamonds inaddition to other stones. 7;

5. A machine as claimed in claim 1 and comprising a driving gear mountedwith its axis normal to the surface of the skaif and meshed with a gearcoaxial with the tangent axis for revolving the stone axis about thetangent axis, another driving gear mounted about the axis normal tothelsurface of the skaif in mesh with a further gear coaxial with thetangent axis about which a third gear is mounted which in turn mesheswith a gear on a dop spindle on which the stone is mounted, for rotatingthe dop spindle and stone about the stone axis.

6. A machine as claimed in claim 1 wherein the stone is mounted on a dopspindle and means are provided for rotating the dop spindle about thestone axis by a flexible shaft.

7. A machine as claimed in claim 1 wherein the stone is mounted on a dopspindle and comprising a flexible shaft adapted to drive a gear meshingwith a gear coaxial with the tangent axis, another gear coaxial with thetangent axis which in turn meshes with a gear on the dop spindle forrotating such about the stone axis.

8 A machine as claimed in claim 1 wherein the stone may be rotated aboutits axis from one cutting contact position to another and means areprovided for temporarily locking the stone against rotation about itsown axis in any selected contact position.

9. A machine as claimed in claim 1 wherein means are provided fortemporarily locking the ston mounting against rotation of its axis aboutthe tangent axis, in any selected position.

10. A machine as claimed in claim 1 wherein means are provided forrevolving the stone and the tangent axis together about an axis normalto the surface of the skaif and comprising temporary locking means forpreventing the revolution of the said axes about the axis normal to thesurface of the skaif.

11. A machine as claimed in claim 1 wherein means are provided forrevolving the stone and the tangent axis together about an axis normalto the surface of the skaif and comprising means for temporarily lockingthe stone mounting,

against revolution of its axis about the tangent axis in any selectedposition.

12. A machine as claimed in claim 1 wherein means are provided foradjusting the stone in the direction of its axis towards or away fromthe cutting plane of the skaif.

FREDERICK CHARLES JEARUM.

